Conventional jigs operate by means of gravity, and may comprise a sieve which is vibrated within a body of water, or a fixed sieve immersed in water which is pulsated. Separation of particles takes place in the jig bed according to specific gravity, the bed consisting of a layer of coarse heavy particles or raging. Particles with high specific gravity penetrate the ragging while particles of low specific gravity are carried away from the ragging by cross flow of water.
In Cross U.S. Pat. No. 4,056,464 there is described a jig in which slurry is introduced on to a rotor on which is held captive, ragging supported on a woven mesh screen, the rotor and screen being of frusto-conical shape. The rotor and screen rotate within a stationary container of water which is pulsed to provide a jigging action supplemented by centrifugal force.
Campbell U.S. Pat. No. 4,279,741 is likewise directed to a centrifugal jig, Campbell employing a cylindrical screen and in one embodiment a rotating chamber.